جریان سیال و انتقال حرارت نانوسیال ها در جاذب حرارت میکروکانال با چیدمان ورودی و خروجی از نوع V Fluid flow and heat transfer of nanofluids in microchannel heat sink with V-type inlet/outlet arrangement

1. Introduction With ever-changing of technology and new horizons being peered in many fields of science, innovative ways have been supported and in the case of the present study, heat transfer techniques have been developed. One of the cases in which the amount of heat transfer and fluid flow has been studied prevalently, is in electronic cooling systems. With the overincreasing furtherance of computing and electronic technology and making devices smaller but faster and more reliable in quality, the heat dissipation from these products is of importance in order to keep them in their desired designation. In most of the cases the chipsets in electronic devices had been cooled using forced air flow convection so far; however, in complex devices with lots of transistors or in high performance electronic chipsets, removing heat from the system is a crucial matter that affects the performance of that system. During the last two decades many efforts have been done to receive high rate of heat transfer from the system and among all of them, microchannel heat sink has got the most consideration due to its small dimension and volume for each heat load but its ability of providing high heat transfer coefficient. Tuckerman and Pease [1] were the first researchers who worked on heat sink by introducing an approach for removing heat from a chip by forcing coolant over closed channels etched onto the backside of a silicon wafer. They stated that the heat transfer coefficient has a reverse proportionality with the channel width. The studies performed in this area are divided into three categories: theoretical, numerical and experimental studies. Knight et al. [2] performed a study to find an optimum heat transfer from the hot surface to the incoming fluid for both laminar and turbulent flow theoretically. They stated that for low pressure loss in the channel, the laminar flow has less thermal resistance than the turbulent one. At the opposite side, the thermal resistance is low in the turbulent region when the pressure drop is considerable. Zhao and Lu [3] presented analytical approaches for heat transfer in a microchannel heat sink called porous medium and fin model. They concluded from their approaches that the Nusselt number increased with the channel aspect ratio increment and decreased with the increase of the effective thermal conductivity ratio. Another analytical study was on modelling of heat transfer and fluid flow in a microchannel heat sink using modified Darcy model [4]. A porous wall condition was selected as the heat sink material for the microchannel. Numerical studies were also conducted such as what Fedorov and Viskanta [5] did in which fluid flow and heat transfer were studied in a three dimensional heat sink microchannel. The Navier-Stokes equations for incompressible laminar flow were applied and the numerical data were validated with experimental data by Pak and Nakayama [6], Kim et al. [7] and Kawano et al. [8,9]. Some researchers performed experimental analysis of fluid flow and heat transfer characteristics along with the numerical approaches in microchannels. Qu and Mudawar [10] studied pressure loss and heat transfer in a copper heat sink both numerically and experimentally. The data achieved from the experiment were in a good agreement with the numerical data. Another example on study in experimental field is that of Tislej et al. [11].